1. Field of the Invention
The present invention relates to an information signal recording apparatus and an information signal reproducing apparatus for several tracks in parallel with one another formed on a recording medium, and in particular to those having features in tracking control for the tracks. For example, the tracking control is used in an apparatus such as a VTR having rotary heads through which video-signals from oblique tracks recorded and formed on a magnetic tape are reproduced.
2. Related Background Art
Heretofore, as a reproducing tracking system for home VTRs, a system (CTL system) in which a stationary magnetic head is provided in a part of a tape path so as to record vertical synchronization signals separated from recording signals upon recording, on an exclusive control track formed longitudinally of a tape, and a system (4fATF system) in which four kinds of pilot signals having relatively low frequencies are circulately recorded on a track, being superposed with main signals such as video signals and audio signals recorded on the same track, by a rotary head for recording and reproducing the main signals, so that cross-talk components reproduced from two adjacent reproducing tracks are compared with each other upon reproduction in order to obtain tracking error signals (ATF signals), have been proposed and put into practice.
However, the above-mentioned CTL system requires a space for the stationary head, and accordingly this system is unadvantageous in view of miniaturization. On the contrary, the 4fATF system is advantageous in view of miniaturization, but is disadvantageous since it requires a complicated circuit arrangement for the four kinds of pilot signals which require several analog circuit elements, and since the pilot signals superposed with digital signals occupy a relative wide band width so as to lower the reliability of the digital signals.
Meanwhile, recently, even for home VTRs, VTRs such as that picture signals in one field are divided and recorded on a plurality of tracks in order to record and reproduce a relatively large volume of information so as to cope with a high image quality and digitalization, have been developed, and accordingly, new tracking systems suitably used for these home VTRs have come under consideration. That is, one of these new tracking systems is such that recording signals are recorded so that frequency components corresponding to a specific kind of pilot signals are contained in modulated signals when digital signals to be recorded is modulated, and the tracking control pilot signals are superposed with the digital signals in a multiplex manner through the above-mentioned modulation.
Referring to FIG. 1A which is a plan view showing a drum of a VTR, a rotary drum 40 comprises a tape 41, a ch-1 head 42 of +azimuth, a ch-2 head 43 of -azimuth, a ch-3 head 44 of +azimuth, and a ch-4 head of -azimuth.
Referring to FIG. 1B which is a front view showing heads that can be seen upon rotation of the drum, for explaining the attachment heights of the heads 42, 45, the ch-1 and ch-2 heads, and ch-3 and ch-4 heads are, in pairs, arranged so as to be adjacent to each other. These pairs are arranged at intervals of an angle of 180 deg. so as to be opposed to each other. As is clear from this figure, the ch-2 and ch-4 heads are offset by a distance h which corresponds to one track pitch on the tape, with respect to the ch-1 and ch-3 heads. With this arrangement, two tracks can be simultaneously recorded or reproduced for every half rotation of the drum, that is, it can cope with a large volume of information.
Next, explanation will be made of the new tracking system with reference to FIG. 2 which is a view illustrating a recording pattern on the tape 41. In order to obtain a tracking error signal, two kinds of pilot signals having frequencies f1, f2 are used, and are superposed with main signals every other track. The rotation of generation of the pilot signals are such that one turn is made through four tracks, and no superposition of the pilot signals occurs on tracks belonging to the heads of +azimuth but pilot signals having f1, f2 are alternately superposed on tracks belonging to the heads of -azimuth. It is noted that reference numerals (1) to (10) denote frame numbers in each of the tracks, that is, signals in one frame are divided and recorded on ten tracks.
As mentioned above, in this example, since four tracks are recorded and reproduced per rotation of the drum, 2.5 turns are required for scanning tracks in one frame, and the pilot rotation and the frame are synchronized with each other by units of two frames (20 tracks).
FIG. 3 is a timing chart showing pilot signals which are superposed with main signals by the heads (ch-1 to ch-4), and the pilot signals which are reproduced from the heads. Explanation will be hereinbelow made with reference to this figure.
In FIG. 3, there are shown a frame signal (a) upon recording or reproduction, a head switch signal (b), pilot timing (c) which is recorded by the ch-1 and ch-3 heads, and which is shown so that it is not superposed, pilot timing (d) which is recorded by the ch-2 and ch-3 heads, which is shown so that pilot signals f1, f2 are alternately recorded, pilot signals (e) which are reproduced by the ch-1 and ch-3 heads in a satisfactory reproducing condition, and reproducing timing (f) of pilot signal components which are similarly reproduced by the ch-2 and ch-3 heads.
As understood from FIG. 2, by setting the head width of each of the heads to be wider than the track pitches, pilot signals recorded on two adjacent tracks can be reproduced in the form of crosstalk at the reproducing timing by the ch-1 and ch-3 heads, and accordingly, this system can provide a tracking error signal (ATF) with the use of such a fact that crosstalk components are equal to each other between the two adjacent tracks if the tracking condition is satisfactory.
FIG. 4 is a block diagram illustrating a circuit for detecting the above-mentioned ATF error signal during reproduction.
Referring to FIG. 4, a head switch signal (HSW) 70 changes over between the reproduced signals from the ch-1 and ch-3 heads in synchronization with the rotation of the drum, a switch circuit 79 changes over between reproduced signals from the ch-1 and ch-3 heads in response to the HSW signal 70, a band-pass filter (BPF) 71 extracts only the reproduced pilot signals f1, f2 from reproduction RF signals, and an amplifier 72 amplifies the reproduced pilot signals which are outputs from the BPF 71. Further, a band pass filter (BPF) 73 extracts only the component f2 from the output of the amplifier 72, a band pass filter (BPF) 74 extracts only the component f1 from the output of the amplifier 72, a detecting circuit for converting the component f2 which is the output of the BPF 73, into a d.c. level, a detecting circuit 76 similarly converts the component f1 into a d.c. level, a differential amplifier circuit 77 receives both detected outputs, and an invertor circuit 78 inverts the signals, and a switch circuit 80 changes over between the output of the differential amplifier 77 and the output of the invertor circuit 78 in response to the HSW 70. A process circuit 81 for reproduced signals in the video-audio system processes the reproduced RF signals so as to provide reproduced video-signals and reproduced audio signals.
Next, explanation will be made of operation. As mentioned above, in the system in this example, the reproduced pilot signals for providing the ATF error signal are included, as crosstalk components from two adjacent tracks (-azimuth track), in the reproduced signals by the ch-1 and ch-3 heads of +azimuth. Accordingly, only the reproduced signals from the ch-1 and ch-3 heads, among the four heads, are required, and the reproduced pilot signals are turned into reproduced signals for only a single system by means of the switch circuit 79. The reproduced signals which contain the main signals are naturally led to the video-audio system reproduction processing circuit 81, and are also applied to the BPF 71 as an ATF circuit for extracting the reproduced pilot signals. Thereafter, the crosstalk components f1, f2 are separated and detected, and are compared by the differential amplifier 77 so as to obtain the ATF error signal for a single system.
Thereafter, the switch circuit 80 selects the invertor circuit 78 upon selection of the ch-3 head, being synchronized with the HSW 70 so as to cope with fore-and-aft positional exchanges of the tracks for the components f1, f2 by the ch-1 and ch-3 heads.
The new tracking system has been hereinabove explained, which will be hereinbelow denoted as "2fATF" as necessary.
Further, as to conventional high speed reproduction such as high speed search of a VTR which carries out analog recording, since the reproduced picture directly corresponds to a position where the reproducing head traces a track, it is common to control the position of the head trace so as to fix a noise bar on an image plane. For this purpose, the magnification of the travel speed of a tape is set to be N (where N is an integer equal to or larger than 2), that is, the travel speed is set to be N times as high as that during reproduction, and a tracking error signal is sample-held in synchronization with the rotation of the head so as to control the rotational speed of a capstan.
That is, during high speed reproduction, a phase reference signal is produced in order to fix a noise bar on an image plane, and a sample-hold pulse is produced from the sample hold circuit for the ATF error signal in synchronization with the rotational phase of the drum. Accordingly, only high speed reproduction having a rotational speed which is N (N is an integer) times as high as that of the drum can be controlled.
On the contrary, more recently, VTRs which can record and reproduce digital signals have been put into practice, and those have been developed as consumer digital VTRs. It is difficult to use a DTF (which is a means in which a head is attached to an actuator such as a bimorph so as to compensate the inclination between a head trace and a track, for preventing lowering of the reproduction RF signal) in a consumer VTR, as is in a business use VTR since it causes the apparatus to be expensive and large-sized. Accordingly, similar to analog VTRs, during high speed search of a digital VTR, a drop of the reproduction signal periodically occurs due to that a head crosses a track.
FIG. 5 shows a head switch pulse HSW and a reproduction RF envelope during a search at a speed which is eleven times as high (in the positive direction). It has been well-known that the reproduction RF signal has a bead-to-bead shape envelope. Further, it has been known that the reproduction level and an error rate for reproduction data greatly affects in digital recording with a certain threshold value. When the above-mentioned threshold value is set to A in FIG. 5, there is a period T during which the reproduction data can be detected, with a period equal to one period (T.sub.0) of the reproduction RF envelopes.
In the digital VTR, video signals are digitalized, and synchronization data and ID information are added for every predetermined unit, and they are recorded on a tape in the form of an assembly of synchronized blocks in a small unit which can be demodulated. During reproduction, the signals are demodulated for every reproduced synchronized block, and are synthesized on a memory corresponding to a monitor screen, which are then delivered.
In consideration with the above-mentioned background, the control for the so-called fixation of a noise bar which has been carried out in the conventional VTR, is not required for the digital VTR, and further, no noise bar flows in a reproduction picture at a tape travel speed other than that of search which is an integer times (N times) as high. Further, on the contrary, an appropriate search speed is not always an integer times as high as that during recording. Accordingly, a problem such that stable control cannot be made when search having a high speed which is not an integer times as high is carried out, has been raised.
Further, in the above-mentioned new tracking system (2fATF system) or a 4fATF system, an ATF error signal having four track periods cannot be obtained, and in a case such that the above-mentioned two frames are recorded in twenty tracks, no tracking control can be made in such a way that a desired head traces a predetermined track in the two frames with a predetermined timing. Thus, there is proposed such a system that track number information in the two frames are mixed as ID with main signals and are recorded, and track jump is made in accordance with a reproduced track number so as to perform just-tracking on a predetermined track in the two frames with an ATF signal by 2fATF.
However, in a system in which a predetermined voltage is temporarily inserted in a tracking signal, as a track-jumping means, if the continuity between the above-mentioned ATF error and the above-mentioned predetermined voltage cannot be taken, stable control cannot be made, and accordingly, a problem such that a reproduced picture becomes unstable for a relatively long time has been raised.